Packaging material for battery case and battery case

ABSTRACT

A packaging material for battery cases according to the present invention including a heat resistant resin oriented film layer  2  constituting an outer layer, a thermoplastic resin non-oriented film layer  3  constituting an inner layer, and an aluminum foil layer  4  disposed between both the film layers is characterized in that as the heat resistant resin oriented film, a heat resistant resin oriented film having a shrinkage percentage of 2 to 20% is used. With this packaging material, excellent formability can be secured without coating slip characteristics imparting components and sufficient volumetric energy density can be obtained.

TECHNICAL FIELD

The present invention relates to a packaging material for battery cases,such as, e.g., lithium-ion secondary battery cases.

In this specification, the wording of “aluminum” is used to include themeaning of an aluminum and its alloy.

BACKGROUND ART

A lithium-ion secondary battery has been widely used as a power sourceof, e.g., a notebook-sized personal computer, a video camera, a cellularphone, or an electric automobile. As such a lithium-ion secondarybattery, a battery in which a periphery of a battery body is coveredwith a case has been used. As the packaging material for cases, forexample, a packaging material in which an outer layer made of anoriented polyamide film, an aluminum foil layer, and an inner layer madeof a non-oriented polypropylene film are integrally bonded in this orderis known (see Patent Document 1).

In such a packaging material for battery cases, since the packagingmaterial is formed into various battery configurations, it is requiredto have high deep drawing formability. In order to give high deepdrawing formability, conventionally, a packaging material in which fattyacid amide series slip characteristics imparting components are coatedon a surface of an outer layer film to enhance the slipping of thematerial in a die at the time of forming (see Patent Document 2) or apackaging material comprising an aluminum foil layer and an outer layerfilm thicker than the aluminum foil layer have been employed.

Patent Document 1: JP 2001-6631, A Patent Document 2: JP 2002-216714, ADISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

In the structure in which fatty acid amide series slip characteristicsimparting components are coated on a surface of an outer layer film,however, there is a problem that a step of coating the slipcharacteristics imparting components is required and therefore theproductivity is low. Furthermore, there is another problem that the slipcharacteristics imparting components will evaporate at the time ofvacuuming or sealing a battery and the evaporated components will adhereto the processing equipment, requiring a cleaning operation for removingthe adhered components, which further decreases the productivity.

Furthermore, in a structure in which the thickness of the outer layerfilm is increased with respect to the thickness of the aluminum foillayer, there is a problem that the volumetric energy density of thebattery deteriorates since the entire thickness of the packagingmaterial increases.

The present invention was made in view of the aforementioned technicalbackgrounds, and aims to provide a packaging material for battery casesand a battery case capable of securing excellent formability withoutcoating slip characteristics imparting components and obtainingsufficient volumetric energy density.

Means to Solve the Problems

In order to attain the aforementioned object, the present inventor hasfound new finding that a shrinkage percentage of a heat resistant resinoriented film layer constituting an outer layer of a packaging materialaffects formability of a packaging material and completed the presentinvention. That is, the present invention provides the following means.

[1] A packaging material for battery cases comprising a heat resistantresin oriented film layer constituting an outer layer, a thermoplasticresin non-oriented film layer constituting an inner layer, and analuminum foil layer disposed between both the film layers,

wherein as the heat resistant resin oriented film, a heat resistantresin oriented film having a shrinkage percentage of 2 to 20% is used.

[2] A packaging material for battery cases comprising a heat resistantresin oriented film layer constituting an outer layer, a thermoplasticresin non-oriented film layer constituting an inner layer, and analuminum foil layer disposed between both the film layers,

wherein as the heat resistant resin oriented film layer, abiaxially-oriented polyamide film having a shrinkage percentage of 2 to20%, a biaxially-oriented polyethylene naphthalate having a shrinkagepercentage of 2 to 20%, or a biaxially-oriented polyethyleneterephthalate having a shrinkage percentage of 2 to 20% is used.

[3] The packaging material for battery cases as recited in theaforementioned Item 1 or 2, wherein the shrinkage percentage of theoriented film is 5 to 10%.

[4] The packaging material for battery cases as recited in any one ofthe aforementioned Items 1 to 3, wherein a thickness of the heatresistant oriented film layer is 12 to 50 μm, a thickness of thethermoplastic resin non-oriented film layer is 20 to 80 μm and athickness of the aluminum foil layer is 5 to 50 μm.

[5] The packaging material for battery cases as recited in any one ofthe aforementioned Items 1 to 4, wherein the heat resistant resinoriented film layer and the aluminum foil layer are integrally laminatedvia a urethane series adhesive layer.

[6] A battery case obtained by subjecting the packaging material asrecited in any one of the aforementioned Items 1 to 5 to deep drawing orstretch forming.

EFFECTS OF THE INVENTION

According to the invention as recited in the aforementioned Item [1],since as the heat resistant resin oriented film layer, a heat resistantresin oriented film having a shrinkage percentage of 2 to 20% is used,the packaging material is excellent in formability of, e.g., deepdrawing and stretch forming. This makes it possible to perform sharp,deep and high configuration forming. Thus, since excellent formabilitycan be secured without requiring coating of slip characteristicsimparting components, it is not required to provide a step of coatingslip characteristics components as required in a prior art, andtherefore it is excellent in productivity. Furthermore, since it is notespecially required to increase the thickness of the outer layer filmwith respect to the thickness of the aluminum foil layer as in a priorart technique, sufficient volumetric energy density can be secured.

According to the invention as recited in the aforementioned Item [2],since as the heat resistant resin oriented film layer constituting anouter layer, a biaxially-oriented polyamide film having a shrinkagepercentage of 2 to 20%, a biaxially-oriented polyethylene naphthalatefilm having a shrinkage percentage of 2 to 20%, or a biaxially-orientedpolyethylene terephthalate film having a shrinkage percentage of 2 to20% is used, it is especially excellent in formability of, e.g., deepdrawing and stretch forming. Thus, it becomes possible to attain sharperand deeper configuration forming. Since excellent formability can besecured without coating slip characteristics imparting components asmentioned above, it is not required to provide a step of coating slipcharacteristics imparting components as required in a prior arttechnique, and thus it is excellent in productivity. Furthermore, sinceit is not especially required to increase the thickness of the outerlayer film with respect to the thickness of the aluminum foil layer asin a prior art technique, sufficient volumetric energy density can besecured.

According to the invention as recited in the aforementioned Item [3],since the shrinkage percentage of the oriented film is to 10%, theformability of, e.g., deep drawing or stretch forming can be improved,which enables higher and deeper configuration forming.

According to the invention as recited in the aforementioned Item [4],generation of pinholes can be sufficiently prevented and cost reductioncan be attained.

According to the invention as recited in the aforementioned Item [5],since the heat resistant resin oriented film layer and the aluminum foillayer are integrally bonded via a urethane series adhesive layer,sharper forming can be attained.

According to the invention as recited in the aforementioned Item [6], itis possible to provide a battery case having a sharp and deepconfiguration.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view showing an embodiment of a packagingmaterial for battery cases according to the present invention;

FIG. 2 is a view showing an example of a production method of apackaging material for battery cases according to the present invention.

DESCRIPTION OF REFERENCE NUMERALS

-   -   1 . . . Packaging material for battery cases    -   2 . . . Outer layer (heat resistant resin oriented film layer)    -   3 . . . Inner layer (thermoplastic resin non-oriented film        layer)    -   4 . . . Aluminum foil layer

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the packaging material 1 for battery cases according tothe present invention is shown in FIG. 1. This packaging material isused as a packaging material for lithium-ion secondary batteries. Thispackaging material 1 for battery cases has a structure in which a heatresistant resin oriented film layer (outer layer) 2 is integrallylaminated on an upper surface of an aluminum foil layer 4 via a firstadhesive layer 5 and a thermoplastic resin non-oriented film layer(inner layer) 3 is integrally laminated on a lower surface of thealuminum foil layer 4 via a second adhesive layer 6.

The heat resistant resin oriented film layer (outer layer) 2 is a memberwhich mainly undertakes a role of securing good formability as apackaging material, i.e., which mainly undertakes a role of preventingbreakage of the aluminum foil due to necking which may sometimes occurat the time of the forming. In this invention, as the heat resistantresin oriented film layer 2, it is necessary to use a heat resistantresin oriented film having shrinkage percentage of 2 to 20%. If theshrinkage percentage is less than 2%, breakage and/or cracks of thepackaging material may occur at the time of performing shape forming,such as, e.g., deep drawing or stretch forming. On the other hand, itthe shrinkage percentage exceeds 20%, detachment of the heat resistantresin oriented film layer 2 and the aluminum foil layer 4 may occurafter performing shape forming, such as, e.g., deep drawing or stretchforming. Among other things, as the heat resistant resin oriented film,if is preferable to use a heat resistant resin oriented film havingshrinkage percentage of 5 to 10%.

Furthermore, as the heat resistant resin oriented film layer 2, it ispreferable to use a biaxially-oriented polyamide film having shrinkagepercentage of 2 to 20%, a biaxially-oriented polyethylene naphthalate(PEN) film having shrinkage percentage of 2 to 20% or abiaxially-oriented polyethylene terephthalate (PET) film havingshrinkage percentage of 2 to 20%. In this case, the formability of,e.g., deep drawing or stretch forming can be further improved, whichenables sharper and deeper configuration forming.

The aforementioned “shrinkage percentage” denotes a size change rate ofa test piece in the oriented direction before and after the immersion ofthe test piece (10 cm×10 cm) of the heat resistant resin oriented film 2in 95° C. hot water for 30 minutes, and can be obtained by the followingequation.

Shrinkage percentage(%)={(X−Y)/X}×100

X: oriented directional size before the immersion treatment

Y: oriented directional size after the immersion treatment

The shrinkage percentage in the case of employing a biaxially-orientedfilm is an average value of the size change rates in two orienteddirections.

The shrinkage percentage of the heat resistant resin oriented film 2 canbe controlled by, for example, adjusting the heat setting temperature atthe time of the stretch processing.

It is preferable that the thickness of the heat resistance resinoriented film layer 2 is set to 12 to 50 μm.

The thermoplastic resin non-oriented film layer (inner layer) 3 is amember for undertaking a role of giving excellent chemical resistanceagainst strong corrosive electrolytic solution used for, e.g.,lithium-ion secondary batteries and also giving heat sealing nature tothe packaging material.

The thermoplastic resin non-oriented film layer 3 is not specificallylimited. But, the layer 3 is preferably constituted by a non-orientedfilm made of at least one of thermoplastic resins selected from thegroup consisting polyethylene, polypropylene, orefin series copolymer,acid modification thereof, and ionomer.

The thickness of the thermoplastic resin non-oriented film layer 3 ispreferably set to 20 to 80 μm. Setting the thickness 20 μm or aboveenables sufficient prevention of generation of pinholes, and setting thethickness 80 μm or below enables reduction of resin amount and costreduction. Among other things, it is more preferable that the thicknessof the thermoplastic resin non-oriented film layer 3 is set to 30 to 50μm.

The heat resistant resin oriented film layer 2 and the thermoplasticresin non-oriented film layer 3 each can be a single layer or a multiplelayer.

The aluminum foil layer 4 is a member for undertaking a role of givinggas barrier nature of preventing intrusion of oxygen and/or watercontent to the packaging material. As the aluminum foil layer 4, a foilmade of pure aluminum or Al—Fe series alloy having a thickness of 5 to50 μm can be preferably used.

The first adhesive layer 5 is not specifically limited. For example,urethane series adhesive layer and acrylic series adhesive layer can beexemplified. Among other things, it is preferable that the firstadhesive layer 5 is a urethane series adhesive layer made of urethaneseries two-component adhesive. In this case, forming can be performedmore sharply.

The second adhesive layer 6 is not specifically limited. For example, anadhesive layer made of resin containing urethane series resin, acrylicresin or thermoplastic elastomer, or acid-modified polyolefin such as,e.g., maleic anhydride acid-modified polyethylene or maleic anhydrideacid-modified polypropylene. The second adhesive layer 6 can be formedby, for example, laminating an adhesive resin film (e.g., acid-modifiedpolyolefin film) on one surface of the thermoplastic resin non-orientedfilm layer 3.

The aforementioned embodiment employs the structure provided with thefirst adhesive layer 5 and the second adhesive layer 6. However, boththe layers 5 and 6 are not essential structural layers. A structure notprovided with these layers can be employed.

The packaging material for battery cases according to the presentinvention can be preferably used as a packaging material for lithium-ionsecondary battery cases which requires high volume energy density, butnot limited to such usage.

By subjecting the packaging material 1 for battery cases according tothe present invention to forming (e.g., deep drawing or stretchforming), a battery case can be obtained.

EXAMPLE

Next, concrete examples of the present invention will be explained, butthe present invention is not specifically limited to these examples.

Example 1

As shown in FIG. 2, while co-extruding a maleic anhydride acid-modifiedpolypropylene layer 21 having a thickness of 3 μm and a non-modifiedpolypropylene layer 22 having a thickness of 12 μm, an aluminum foil 4(AA8079-O material) having a thickness of 40 μm was supplied from theleft side of FIG. 2 and a non-oriented film 3 having a thickness of 30μm made of polypropylene was supplied from the right side of FIG. 2, andthe aluminum foil 4 and the non-oriented film 3 were laminated with theco-extruded maleic anhydride acid-modified polypropylene layer 21 andnon-modified polypropylene layer 22 disposed therebetween with a pair ofheating pressure rollers.

Next, on the surface of the aluminum foil 4 of the obtained laminatedfilm, urethane series resin adhesive 5 was applied with a gravure roll,and then the adhesive was dried to some degree by heat. Thereafter, onthe adhesive surface, a biaxially-oriented film 2 made of nylon having athickness of 25 μm and shrinkage percentage of 10% was laminated. Thus,a packaging material for battery cases was obtained.

Example 2

A packaging material for battery cases was obtained in the same manneras in Example 1 except that a biaxially-oriented film made of nylonhaving a thickness of 15 μm and shrinkage percentage of 15% was used inplace of the biaxially-oriented film made of nylon having a thickness of25 μm and shrinkage percentage of 10%.

Example 3

A packaging material for battery cases was obtained in the same manneras in Example 1 except that a biaxially-oriented film made of nylonhaving a thickness of 15 μm and shrinkage percentage of 7% was used inplace of the biaxially-oriented film made of nylon having a thickness of25 μm and shrinkage percentage of 10%.

Comparative Example 1

A packaging material for battery cases was obtained in the same manneras in Example 1 except that a biaxially-oriented film made of nylonhaving a thickness of 25 μm and shrinkage percentage of 1% was used inplace of the biaxially-oriented film made of nylon having a thickness of25 μm and shrinkage percentage of 10%.

Comparative Example 2

A packaging material for battery cases was obtained in the same manneras in Example 1 except that a biaxially-oriented film made of nylonhaving a thickness of 25 μm and shrinkage percentage of 25% was used inplace of the biaxially-oriented film made of nylon having a thickness of25 μm and shrinkage percentage of 10%.

Example 4

A packaging material for battery cases was obtained in the same manneras in Example 1 except that a biaxially-oriented film made ofpolyethylene telephthalate (PET) having a thickness of 12 μm andshrinkage percentage of 18% was used in place of the biaxially-orientedfilm made of nylon having a thickness of 25 μm and shrinkage percentageof 10%.

Example 5

A packaging material for battery cases was obtained in the same manneras in Example 1 except that a biaxially-oriented film made ofpolyethylene telephthalate (PET) having a thickness of 20 μm andshrinkage percentage of 5% was used in place of the biaxially-orientedfilm made of nylon having a thickness of 25 μm and shrinkage percentageof 10%.

Example 6

A packaging material for battery cases was obtained in the same manneras in Example 1 except that a biaxially-oriented film made ofpolyethylene telephthalate (PET) having a thickness of 12 μm andshrinkage percentage of 8% was used in place of the biaxially-orientedfilm made of nylon having a thickness of 25 μm and shrinkage percentageof 10%.

Comparative Example 3

A packaging material for battery cases was obtained in the same manneras in Example 1 except that a biaxially-oriented film made ofpolyethylene telephthalate (PET) having a thickness of 12 μm andshrinkage percentage of 1% was used in place of the biaxially-orientedfilm made of nylon having a thickness of 25 μm and shrinkage percentageof 10%.

Comparative Example 4

A packaging material for battery cases was obtained in the same manneras in Example 1 except that a biaxially-oriented film made ofpolyethylene telephthalate (PET) having a thickness of 12 μm andshrinkage percentage of 25% was used in place of the biaxially-orientedfilm made of nylon having a thickness of 25 μm and shrinkage percentageof 10%.

Example 7

A packaging material for battery cases was obtained in the same manneras in Example 1 except that a biaxially-oriented film made ofpolyethylene naphthalate (PEN) having a thickness of 25 μm and shrinkagepercentage of 10% was used in place of the biaxially-oriented film madeof nylon having a thickness of 25 μm and shrinkage percentage of 10%.

Example 8

A packaging material for battery cases was obtained in the same manneras in Example 1 except that a biaxially-oriented film made ofpolyethylene naphthalate (PEN) having a thickness of 15 μm and shrinkagepercentage of 15% was used in place of the biaxially-oriented film madeof nylon having a thickness of 25 μm and shrinkage percentage of 10%.

Example 9

A packaging material for battery cases was obtained in the same manneras in Example 1 except that a biaxially-oriented film made ofpolyethylene naphthalate (PEN) having a thickness of 15 μm and shrinkagepercentage of 7% was used in place of the biaxially-oriented film madeof nylon having a thickness of 25 μm and shrinkage percentage of 10%.

Comparative Example 5

A packaging material for battery cases was obtained in the same manneras in Example 1 except that a biaxially-oriented film made ofpolyethylene naphthalate (PEN) having a thickness of 25 μm and shrinkagepercentage of 1% was used in place of the biaxially-oriented film madeof nylon having a thickness of 25 μm and shrinkage percentage of 10%.

Comparative Example 6

A packaging material for battery cases was obtained in the same manneras in Example 1 except that a biaxially-oriented film made ofpolyethylene naphthalate (PEN) having a thickness of 25 μm and shrinkagepercentage of 25% was used in place of the biaxially-oriented film madeof nylon having a thickness of 25 μm and shrinkage percentage of 10%.

TABLE 1 Structure of outer layer (oriented film) Formability ThicknessShrinkage 6 mm 5 mm 4 mm 3 mm Occurrence of Resin (μm) percentage (%)processed processed processed processed detachment Comp. Example 1 Nylon25 1 x x Δ ∘ Nil Example 1 Nylon 25 10 ∘ ∘ ∘ ∘ Nil Example 2 Nylon 15 15Δ ∘ ∘ ∘ Nil Example 3 Nylon 15 7 Δ ∘ ∘ ∘ Nil Comp. Example 2 Nylon 25 25∘ ∘ ∘ ∘ Detached Comp. Example 3 PET 12 1 x x x ∘ Nil Example 4 PET 1218 Δ Δ ∘ ∘ Nil Example 5 PET 20 5 Δ Δ ∘ ∘ Nil Example 6 PET 12 8 Δ Δ ∘ ∘Nil Comp. Example 4 PET 12 25 x x Δ ∘ Detached Comp. Example 5 PEN 25 1x x x ∘ Nil Example 7 PEN 25 10 Δ Δ ∘ ∘ Nil Example 8 PEN 15 15 Δ Δ ∘ ∘Nil Example 9 PEN 15 7 Δ Δ ∘ ∘ Nil Comp. Example 6 PEN 25 25 x Δ ∘ ∘Detached

As to each packaging material for battery cases obtained as mentionedabove, performance was evaluated based on the following evaluationmethod.

<Evaluation Method of Formability>

A packaging material was formed into a blank configuration 110×180 mmand subjected to one step deep drawing with a straight die having a freeforming height, and the formability was evaluated every forming height(6 mm, 5 mm, 4 mm, 3 mm) as follows. “◯” denotes no crack was generated,“Δ” denotes although cracks were generated at small portions but almostno crack was generated, and “x” denotes cracks were generated almost atthe entire surface. The punch shape of the die employed was 60 mm inlong side, 45 mm in short side, 1-2 mm in corner R, 1-2 mm in punchshoulder, and 0.5 mm in die shoulder.

<Evaluation of Occurrence of External Surface Detachment>

The formed article (processed goods 3 mm formed height) obtained by theone step deep drawing was left in a dryer at 80° C. for 3 hours, andthen visual inspection was performed to find whether the outer surfacelayer caused delamination (detachment).

As will be apparent from the Table, the packaging materials for batterycases of Examples 1 to 9 were excellent in formability and capable offorming sharp and deep configuration. Furthermore, no detachment of theouter surface layer occurred.

To the contrary, in Comparative Examples 1, 3 and 5 in which theshrinkage percentage was less than 2%, the formability was insufficient.Furthermore, in Comparative Examples 2, 4 and 6 in which the shrinkagepercentage exceeded 20%, delamination of the outer layer occurred.

This application claims priority to Japanese Patent Application No.2005-154883 filed on May 27, 2005, the entire disclosure of which isincorporated herein by reference in its entirety.

The terms and expressions which have been employed herein are used asterms of description and not of limitation of this invention. It isrecognized that various any modifications are possible within the scopeof the invention claimed so long as they do not extend beyond the spiritof the invention.

INDUSTRIAL APPLICABILITY

A packaging material for battery cases can be used for, e.g., apackaging material for battery cases, such as, e.g., lithium-ionsecondary battery cases.

1. A packaging material for battery cases comprising a heat resistantresin oriented film layer constituting an outer layer, a thermoplasticresin non-oriented film layer constituting an inner layer, and analuminum foil layer disposed between both the film layers, wherein asthe heat resistant resin oriented film, a heat resistant resin orientedfilm having a shrinkage percentage of 2 to 20% is used.
 2. A packagingmaterial for battery cases comprising a heat resistant resin orientedfilm layer constituting an outer layer, a thermoplastic resinnon-oriented film layer constituting an inner layer, and an aluminumfoil layer disposed between both the film layers, wherein as the heatresistant resin oriented film layer, a biaxially-oriented polyamide filmhaving a shrinkage percentage of 2 to 20%, a biaxially-orientedpolyethylene naphthalate having a shrinkage percentage of 2 to 20%, or abiaxially-oriented polyethylene terephthalate having a shrinkagepercentage of 2 to 20% is used.
 3. The packaging material for batterycases according to claim 1, wherein the shrinkage percentage of theoriented film is 5 to 10%.
 4. The packaging material for battery casesaccording to claim 1, wherein a thickness of the heat resistant orientedfilm layer is 12 to 50 μm, a thickness of the thermoplastic resinnon-oriented film layer is 20 to 80 μm and a thickness of the aluminumfoil layer is 5 to 50 μm.
 5. The packaging material for battery casesaccording to claim 1, wherein the heat resistant resin oriented filmlayer and the aluminum foil layer are integrally laminated via aurethane series adhesive layer.
 6. A battery case obtained by subjectingthe packaging material according to claim 1 to deep drawing or stretchforming.